Various exemplary embodiments of the present invention relate to methods for recovering isoprene from a fermented gas and methods for producing purified isoprene.
Fermentation is a known method for producing isoprene. Production of isoprene by the fermentation method can be carried out by culturing a microorganism having an ability to produce isoprene, such as Bacillus subtilis, as described in U.S. Pat. No. 5,849,970. Isoprene is volatile and has a low solubility in water—0.6 g/L. Thus, isoprene is not a product that accumulates in a culture broth, but instead is present in a fermented gas.
As a unit operation for recovering isoprene from a fermented gas, an absorption method has been known. The absorption method generally includes: i) introducing a fermented gas into an absorption tower and contacting the fermented gas and an absorption solvent so that the isoprene in the fermented gas is absorbed into the absorption solvent, ii) discharging the fermented gas, after contacting the absorption solvent, from the top part of the absorption tower, iii) flash-evaporating the absorption solvent, which has absorbed isoprene, in a vacuum container to recover isoprene, and iv) returning the absorption solvent, after recovery of isoprene, to the absorption tower and using the recycled absorption solvent. Absorption solvents used to recover isoprene in the absorption method have included an isoparaffinic solvent, as described in WO2011/075534 and WO2010/099550, and a hydrocarbon solvent having a 6 to 10 carbon atoms, as described in WO2012/143341.
Cooling is a further known technique of recovering isoprene from a fermented gas. For example, WO2010/101855 proposes a method for liquefying and recovering isoprene by cooling a fermented gas to −35° C. or less.